1. Field of the invention
This invention relates to panels for forming a floor covering, to a method for manufacturing such panels, and to a granulate applied therewith.
More particularly, the invention relates to panels comprising at least a layer, more particularly a substrate layer, of thermoplastic material. Further, such panels may also comprise, above said layer, at least a top layer with a printed decor and a translucent or transparent wear layer.
In particular, the present invention relates to panels of the type which, on two or more opposite edges, comprises coupling means or coupling parts with which two of such floor panels can be coupled at said edges in such a manner that they are mutually locked in a horizontal direction perpendicular to the respective edge and in the plane of the floor panels, as well as in a vertical direction perpendicular to the plane of the floor panels. Such floor panels can be applied for composing a so-called floating floor covering, wherein the floor panels are connected to each other at their edges, however, lie freely on the underlying surface.
2. Related art
Such panels are known, for example, from EP 1 938 963, EP 2 339 092 A1 and WO 2010/023042. From these documents, more particularly vinyl-based floor panels are known for forming a floating floor covering. Such vinyl-based floor panels mostly have a thickness of 3 to 5 millimeters and have a high material density. The respective core of the panels is composed of one or more layers of thermoplastic material, for example, soft PVC, which can comprise fillers. Above the print, a transparent thermoplastic layer and possibly a superficial layer of lacquer are provided. According to EP 2 339 092 A1, a reinforcing layer on the basis of glass fiber can be applied.
The panels of the state of the art show the disadvantage that they are strongly subjected to shrinkage and expansion under the influence of temperature. Shrinkage and expansion may lead to that the floor covering or the individual panels are pushed upward, and, for example, to a mutual release of the coupling parts, or to the phenomenon that the individual panel-shaped elements will drift apart, whereby gaps may occur. The features of the panels of the state of the art are such that problems may occur already with warming due to incident sunlight, for example, at a window in a room.
From WO 2012/004701, it is known to apply a glass fiber layer or embedded profiles for increasing the dimensional stability of such panels. In particular, here the bending stiffness of the panels has been tackled.
U.S. Pat. No. 6,306,318 describes a method for recycling discarded carpets, wherein, starting from a molten mixture of a recyclate on the basis of discarded carpets and fresh soft PVC, flexible floor tiles having a minimum thickness of approximately 5 millimeters are produced by means of an injection molding process. The mixture comprises an amount of plasticizers of maximum 5 percent by weight. The obtained floor tiles have a uniform composition across their thickness and comprise 10 to 20 percent by weight of unmelted carpet fibers of polyamide or polyester, which are distributed uniformly across the thickness of these tiles. The fibers provide for a wear-resistant surface. As an alternative for the recyclate of discarded carpets, also recyclate of glass fiber-reinforced synthetic material (English: fiberglass) can be applied. In the case of carpet, it is started with carpet fibers of approximately 3.2 millimeters or more, wherein a reduction of the length during the process is avoided as much as possible. However, it can be expected that disintegrating the carpets and processing them in the extruder prior to injection molding in fact will lead to shortening the present fibers. It is unclear what the length of the glass fibers will be when starting from a recyclate of glass fiber-reinforced synthetic material. Further, it is unclear how many glass fibers will have been incorporated into the matrix of the tile and which type of glass fiber is applied. The obtained tile is relatively hard and the flexibility leaves much to be desired. This may lead to problems with the impact sound during use and an incapability of adapting to unevennesses of the underlying surface. The injection-molded tile comprises coupling means along the edges, however, these do not provide for a locking in vertical direction. Moreover, the precision of injection molding, in particular in the case of soft thermoplastic materials, is inferior. This method is time-consuming, and moreover there is little possibility of variation in the appearance of the wear side of the tiles. Such tiles possibly still show a strong dimensional change with changing temperature.
GB 1 248 060 describes, as an alternative of a method similar to that of U.S. Pat. No. 6,306,318, the possibility of manufacturing reinforced thermoplastic materials by means of a method wherein continuous fiber layers are stacked and pressed alternating with thermoplastic granulate layers. In this manner, a disintegration of the present fibers in the extruder is avoided. According to the examples, hard PVC can be applied as thermoplastic material.